Engines with direct fuel injection may use high pressure fuel pumps to provide sufficient fuel pressure to the injectors. In some examples, the high pressure fuel pump may be driven by a cam lobe on the engine camshaft. In some cases, such a fuel pump drive lobe may be integrated into the camshaft where the valve timing is being actively phased during engine operation.
The inventors of the present application have recognized a problem in such previous approaches in that the fuel pump is typically driven “downstream” (in terms of power flow) of hydraulic actuators used to actively adjust timing of the intake and exhaust cams. For example, in previous approaches, the fuel pump may be driven at a camshaft side of a variable cam timing (VCT) actuator, whereas the VCT actuator is driven at the crankshaft side of the actuator by the crankshaft, e.g., via a timing chain. In such situations, when adjusting the phasing of the VCT actuator, the actuator may have to work against significant resistance by the fuel pump. Therefore, actuating a high pressure fuel pump in such a manner may adversely affect transient control of the valve timing, for example, by significantly decreasing the shifting velocity of the VCT actuator. If the shift velocity becomes too low, the performance, emissions and fuel economy of the engine may be degraded.
In one example, some of the above issues may be addressed by a system for an engine driven by an engine crankshaft. Such a system may include a first variable cam device including a first hydraulic actuator, and a second variable cam device including a second hydraulic actuator. The system may further include an intermediate power transfer mechanism, such as a gear or drive shaft, coupled between the first variable cam device and the second variable cam device upstream, in a direction of power flow from the engine crankshaft, of the first hydraulic actuator and the second hydraulic actuator. The system may further include an auxiliary device, such as a fuel pump, coupled to and driven by the intermediate power transfer mechanism.
In this way, the resistance torque of the fuel pump actuation may be located upstream of the first and second hydraulic actuators (e.g., at a sprocket side of the VCT actuators). As such, adjustment of the variable camshafts, for example variable cam timing, may be more accurately provided since adjustments to the camshaft are not required to overcome the fuel pump resistance torque.
Further, the fuel pump drive system may serve as a secondary timing drive coupling the housings of the first and second VCT devices, as well as the drive for the fuel pump. In the example of the drive shaft, it may rotationally couple a first and second camshaft in an overhead camshaft configuration, and thus a timing chain or belt between the two camshafts can be eliminated. Moreover, the claimed configuration can be packaged to fit between the intake and exhaust camshafts, where given the physical constraints of the configuration, a chain may not be suitable.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.